"The volume of the oceans and their seas is nearly 1.5 × 109 [sic] cubic kilometers"

1.5billion km3

You've heard it all before: 70 percent of the earth is covered in water! But what does that really mean? These waters that are spoken of have a breakdown into five different categories: Oceans, rivers, lakes, groundwater, and ice. As an essential part of our daily diet, water is vital for the survival of our ecosystem. The world's oceans comprise 97.3% of the total water on earth and consists of 5 oceans: Atlantic, Pacific, Indian, Arctic, and Southern. The current range for the volume of the world's ocean is from 1.3 to 1.5 billion cubic kilometers and it will still get larger and larger as time passes.

There are two origins of water: comets (extraterrestrial bombardment) and out gassing (condensation of steam from early volcanism). These processes are continuing today. It is estimated that the volume of the earth's ocean increases by 1 cubic meter every year.

"The world ocean covers 71 percent of the earth's surface, or about 361 million sq km (140 million sq mi). Its average depth is 5,000 m (16,000 ft), and its total volume is about 1,347,000,000 cu km (322,300,000 cu mi)."

We as humans don't realize the significance of water on earth. Its not just
coincidence that nearly three-fourths of the Earth is covered with water. This
amount is necessary for earth's natural processes to occur and therefore sustain
life on Earth, not only for humans but also animals, plants and other organisms.
If this isn't interesting enough then this might raise a few brows. If mined,
all the gold suspended in the world's oceans and seas would give each person on
earth 9 pounds.

The volume of the Earth's oceans is approximately 1.3 × 109 km3.
The largest of the oceans is the Pacific Ocean followed by Atlantic, Indian and
Arctic Ocean. Given their sheer volume, 99 percent of the living space on the
planet is found in the oceans. If species are removed from the ecosystem, the
web of relationships is disrupted. Whether most people realize it or not, humans
are part of the world's ecosystems for our most basic needs, including food, medicines,
pure water, and the even the air we breathe.

The average depth of the oceans is 2.5 miles (4 km). The deepest
point lies in the Mariana Trench, 6.8 miles (10.9 km) down. By the way
in comparison, Mount Everest is only 5.5 miles (8.8 km) high. Climbing
up to Mt. Everest provides an extremely dangerous challenge, but try reaching
the depths of the Mariana Trench where the pressure is extremely high and temperature
very low. At the deepest point in the ocean the pressure is more than 8 tons per
square inch, or the equivalent of one person trying to support 50 jumbo jets.
At 4 °C (39 °F), the temperature of almost all of the deep ocean
is only a few degrees above freezing.

The Earth is rather unique than all the other planets in our solar system.
No other planet has liquid water and thus is one of the problems of not being
able to live on Mars.

"Water is not only fascinating, but it is also one of the most important and ubiquitous substances on Earth. There are
1.3 × 109 km3 of water in the oceans,
3.3 × 107 km3 in the polar ice caps,
2 × 105 km3 in glaciers,
105 km3 in lakes, and
1.2 × 103 km3 in rivers. In addition,
2.2 × 105 km3 of water fall annually as precipitation."